Fibre channel port by-pass selector section for dual ported disk drives

ABSTRACT

A data storage system having a plurality of disk drives. Each one has a pair of bidirectional ports. A pair of directors controls the flow of data to and from the disk drives. A first fibre channel port by-pass selector section is provided. The first fibre channel port by-pass selector section includes: an input/output port coupled to a first one of the directors; and, a plurality of output/input ports connected between a first one of the ports of the plurality of disk drives through a first plurality of fibre channel links. The first fibre channel port by-pass selector section is adapted to couple the first one of the directors serially to one, or ones, of the first ports of the plurality of disk drives through a first fibre channel selectively in accordance with a control signal fed to the first fibre channel by-pass selector section. The first fibre channel includes one, or more, of the first plurality of fibre channel links. A second fibre channel port by-pass selector section is provided having an input/output port coupled to a second one of the directors and a plurality of output/ports serially connected between a second one of the pair of ports of the plurality of disk drives through a second plurality of fibre channel links. The second fibre channel port by-pass selector section is adapted to couple the second one of the directors serially to one, or ones, of the second ports of the plurality of disk drives through a second fibre channel selectively in accordance with the control signal. The second fibre channel includes one, or more, of the second plurality of fibre channel links.

BACKGROUND OF THE INVENTION

This invention relates generally to data storage systems and moreparticularly to data storage systems having a plurality of magneticstorage disk drives in a redundancy arrangement whereby the disk drivesare controllable by first disk controllers and second disk controllers.Still more particularly, the invention also relates to systems of suchtype wherein the disk drives are coupled to the disk controllers througha series, unidirectional, “ring” or, fibre channel protocol,communication system.

As is known in the art, in one type of data storage system, data isstored in a bank of magnetic storage disk drives. The disk drives, andtheir coupled interfaces, are arranged in sets, each set beingcontrolled by a first disk controller and a second disk controller. Moreparticularly, in order to enable the set of disk drives to operate inthe event that there is a failure of the first disk controller, each setis also coupled to a second, or redundant disk controller. Therefore, ifeither the first or second disk controller fails, the set can beaccessed by the other one of the disk controllers.

While today, most disk storage systems of this type use a Small ComputerSystem Interconnection (SCSI) protocol, in order to operate with higherdata rates, other protocols are being introduced. One higher data rateprotocol is sometimes referred to as a fibre channel (FC) protocol. SuchFC channel protocol uses a series, unidirectional, “ring” communicationsystem. In order to provide for redundancy, that is, to enable use ofthe set of disk drives in the event that the first disk controllerfails, as discussed above, the set is coupled to the second, orredundant disk controller, using a separate, independent, “ring”, orfibre channel communication protocol. Thus, two fibre channels areprovided for each set of disk drives and their disk interfaces; a firstfibre channel and a second fibre channel.

As is also known, when using the fibre channel communication protocol,if any element in the channel becomes inoperative, the entire channelbecomes inoperative. That is, if the first disk controller becomesinoperative, or if any one of the disk drives in the set coupled to thefirst channel becomes inoperative (i.e., as where the disk interfacefails, the disk interface is inoperative, or removed with its coupleddisk drive, or where the disk drive coupled thereto fails, or isremoved), the first fibre channel, is “broken”, or open, and becomesinoperative. The data stored in the entire portion of the set of diskdrives coupled to the first disk channel is therefore unavailable untilthe inoperative first disk controller or inoperative disk drive isreplaced. This is true with either the first channel or the secondchannel. One technique suggested to solve this problem is through theuse of a switch, sometimes referred to as an LRC (i.e., a loopresiliency circuit) switch. Such LRC switch is used to remove aninoperative disk drive from its channel.

In one suggested arrangement, a printed circuit board is provided foreach disk drive. The printed circuit board has a pair of LRCs, one forthe first channel and one for the second channel. Thus, the open channelmay be “closed” in the event of an inoperative disk drive by placing theLRC thereof in a by-pass condition. While such suggested techniquesolves the inoperative disk drive, or open channel problem, if one ofthe pair of LRCs fails, the entire printed circuit board having the pairof LRCs must be replaced thereby disrupting both the first and secondchannels; and, hence, disrupting the operation of the entire datastorage system.

One technique suggested to solve this disruption problem requires n LRCswitches (where n is the number of disk drives in the set) in the firstchannel, i.e., one LRC for each one the n disk drives in the set andanother n LRC switches in the second channel for each one of the n diskdrives in the second channel. The first channel set of n LRCs is mountedon one printed circuit board and the second channel set of n LRCs ismounted on a different printed circuit board. A backplane is used tointerconnect the two LRC printed circuit boards, the associatedmultiplexers, and the disk drives. In order to provide the requisiteserial, or sequential, fibre channel connections, an elaborate, complex,fan-out wiring arrangement has been suggested for the backplane.Further, the slots provided for the two LRC boards eliminates two diskdrives, and the disk interfaces which would otherwise be plugged intothese two slots of the backplane.

Another fibre channel arrangement is described in U.S. Pat. No.5,729,763 entitled “Data Storage System”, inventor Eli Leshem, issuedMar. 17, 1998, assigned to the same assignee as the present invention.

SUMMARY OF THE INVENTION

In accordance with one feature of the invention, a data storage systemis provided having a plurality of disk drives. Each one has a pair ofports. A pair of directors is included for controlling the flow ofinformation (i.e, data) to and from the disk drives. A first fibrechannel port by-pass selector section is provided. The first fibrechannel selector section includes: an input/output port coupled to afirst one of the directors; and, a plurality of output/input portsconnected between a first one of the ports of the plurality of diskdrives through a first plurality of fibre channel links. The first fibrechannel port by-pass selector section is adapted to couple the first oneof the directors serially to one, or ones, of the first ports of theplurality of disk drives through a first fibre channel selectively inaccordance with a control signal fed to the first fibre channel by-passselector. The first fibre channel includes one, or more, of the firstplurality of fibre channel links. A second fibre channel port by-passselector section is provided having an input/output port coupled to asecond one of the directors and a plurality of output/ports seriallyconnected between a second one of the pair of ports of the plurality ofdisk drives through a second plurality of fibre channel links. Thesecond fibre channel port by-pass selector section is adapted to couplethe second one of the directors serially to one, or ones, of the secondports of the plurality of disk drives through a second fibre channelselectively in accordance with the control signal. The second fibrechannel includes one, or more, of the second plurality of fibre channellinks.

BRIEF DESCRIPTION OF THE DRAWING

These and other features of the invention will become more readilyapparent from the follow detailed description when read together withthe accompanying drawings, in which:

FIG. 1 is a block diagram of a data storage system according to theinvention;

FIG. 2 is a block diagram of a redundant fibre channel network used inthe system of FIG. 1 according to the invention;

FIG. 3 is a block diagram of a port by-pass section used in theredundant fibre channel network of FIG. 3 coupled to a bank of diskdrives used in the system of FIG. 1 according to the invention;

FIGS. 4, 4A, and 4B are block diagrams of the system of FIG. 1 arrangedin an expanded configuration according to the invention;

FIGS. 5, 5A and 5B are block diagrams of a redundant fibre channelnetwork adapted for use in the system of FIG. 1 according to theinvention;

FIGS. 5C-5G are diagrams of the network of FIGS. 5, 5A and 5B configuredin a number of contracted configurations according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, a data storage system 10 is shown wherein ahost computer 12 is coupled to a bank 14 of disk drives through a systeminterface 16. The system interface 16 includes a cache memory 18, havinghigh memory address sections 18H and low address memory sections 18L. Aplurality of directors 20 ₀-20 ₁₅ is provided for controlling datatransfer between the host computer 12 and the bank 14 of disk drives assuch data passes through the cache memory 18. A pair of high addressbusses TH, BH is electrically connected to the high address memorysections 18H. A pair of low address busses TL, BL electrically connectedto the low address memory sections 18L. The cache memory 18 has aplurality of storage location addresses. Here, the storage locationshaving the higher addresses are in the high address memory sections 18Hand the storage locations having the lower addresses are in the lowaddress memory sections 18L. It should be noted that each one of thedirectors 20 ₀-20 ₁₅ is electrically connected to one of the pair ofhigh address busses TH, BH and one of the pair of low address busses TL,BL. Thus, each one of the directors 20 ₀-20 ₁₅ is able to address alllocations in the entire cache memory 18 (i.e., to both the high addressmemory sections 18H and the low address memory sections 18L) and istherefore able to store data in and retrieve data from any storagelocation in the entire cache memory 18.

More particularly, a rear-end portion of the directors, here directors20 ₀-20 ₃ and 20 ₁₂-20 ₁₅, is electrically connected to the bank 14 ofdisk drives through fibre channel (FC) port by-pass sections 23 ₁-23 ₈(described in more detail in connection with FIG. 3), respectively. anda front-end portion of the directors, here directors 20 ₄-20 ₁₁, iselectrically connected to the host computer 12 through I/O adapter cards22 ₁-22 ₈, respectively, as indicated. It should also be noted that eachend of the busses TH, TL, BH, BL terminates in a pair of master andslave arbiters bus arbiters, not shown, as described in co-pendingpatent application Ser. No. 09/224,194 filed Dec. 30, 1998, entitledDATA STORAGE SYSTEM, inventor Mark Zani, assigned to the same assigneeas the present invention, now abandoned, the entire subject matterthereof being incorporated herein by reference.

In operation, when the host computer 12 wishes to store data, the hostcomputer 12 issues a write request to one of the front-end directors 20₄-20 ₁₁ to perform a write command. One of the front-end directors 20₄-20 ₁₁ replies to the request and asks the host computer 12 for thedata. After the request has passed to the requesting one of thefront-end directors 20 ₄-20 ₁₁, the director determines the size of thedata and reserves space in the cache memory 18 to store the request. Thefront-end director then produces control signals on either a highaddress memory bus (TH or BH) or a low memory address bus (TL, BL)connected to such front-end director depending on the location in thecache memory 18 allocated to store the data and enable the transfer tothe cache memory 18. The host computer 12 then transfers the data to thefront-end director. The front-end director then advises the hostcomputer 12 that the transfer is complete. The front-end director looksup in a Table, not shown, stored in the cache memory 18 to determinewhich one of the rear-end directors 20 ₀-20 ₃ and 20 ₁₂-20 ₁₅ is tohandle this request. The Table maps the host computer 12 address into anaddress in the bank 14 of disk drives. The front-end director then putsa notification in a “mail box” (not shown and stored in the cache memory18) for the rear-end director which is to handle the request, the amountof the data and the disk address for the data. Other rear-end directorspoll the cache memory 18 when they are idle to check their “mail boxes”.If the polled “mail box” indicates a transfer is to be made, therear-end director processes the request, addresses the disk drive in thebank, reads the data from the cache memory and writes it into theaddresses of a disk drive in the bank 14. When data is to be read fromthe disk drive to the host computer 12 the system operates in areciprocal manner.

Each one of the rear-end portion of the directors 20 ₀-20 ₃ is identicalin construction and are described in detail in the above-referencedco-pending patent application Ser. No. 09/224,194 (now abandoned) toinclude a pair of central processing sections, CPU X and CPU Y, a dualport random access memory (RAM), and shared resources (Flash memories,etc,) coupled to the bank 14 of disk drives (FIG. 1) through the fibrechannel (FC) port by-pass sections (FIG. 3), as indicated and to a highmemory address bus, here TH, and low memory address bus, here BL. Itshould be noted that the director 20 ₀-20 ₃ and 20 ₁₂-20 ₁₅ has a firstoutput port, A, and a second output port, B. Further, it should be notedthat different pairs of the rear-end directors 20 ₀, 20 ₁; 20 ₂, 20 ₃;20 ₁₂, 20 ₁₃ (not shown); and, 20 ₁₄, 20 ₁₅ are arranged in redundantfibre channel (FC) networks 25 ₁-25 ₄, respectively, as indicated. Stillfurther, it is noted that each one of the redundant fibre channel (FC)networks 25 ₁-25 ₄ also includes pairs of the fibre channel (FC) portby-pass sections 23 ₁, 23 ₂; 23 ₃, 23 ₄; 23 ₅ (not shown), 23 ₆ (notshown); and, 23 ₇, 23 ₈, respectively, as indicated and disk drive sets14 ₁, 14 ₂; 14 ₃, 14 ₄; 14 ₅ (not shown), 14 ₆ (not shown); and, 14 ₇,14 ₈, respectively, as indicated. Each one of the pairs of the redundantfibre channel (FC) networks 25 ₁-25 ₄ is identical in construction, anexemplary one thereof, here redundant fibre channel (FC) networks 25 ₁is shown in detail in FIG. 2.

Thus, as shown in FIG. 2, the first port A and second port B of director20 ₀ is connected to both FC port by-pass section 23 ₁ and to FC portby-pass section 23 ₂. Likewise, the first port A and second port B ofdirector 20 ₁ is connected to both FC port by-pass section 23 ₁ and toFC port by-pass section 23 ₂. More particularly, both directors 20 ₀ and20 ₁ of the redundant FC network 25 ₁ are connected to the pair of FCport by-pass sections 23 ₁, 23 ₂. Each one of the FC port by-passsections 23 ₁, 23 ₂ includes a pair of FC port by-passes 34 ₁ and 34 ₂.Each one of the FC port by-passes 34 ₁ and 34 ₂ is connected to acorresponding one of a plurality of sets 14 ₁, 14 ₂ of the disk drivesin the bank of disk drives 14 (FIG. 1). Each one of the FC portby-passes 34 ₁, 34 ₂ and is identical in construction, an exemplary onethereof, here FC port by-pass 34 ₁ being shown in detail in FIG. 3connected to set 14 ₁ of the disk drives and to directors 20 ₀ and 20 ₁.It is noted that director 20 ₀ is connected to busses TH and BL and thatdirector 20 ₁ is connected to busses TL and BH. Thus, the redundant FCnetwork 25 ₁ (FIG. 1) is connected to all four busses TH, BH, TL, andBL.

More particularly, and referring again also to FIG. 2, it is noted thateach one of the disk drive sets 14 ₁, 14 ₂ includes a plurality of, herefor example eight, disk drives 19 ₁-19 ₈, it being understood that thenumber of disk drives 19 in a set can be selected in accordance with therequisite storage requirements. It is also noted that each one of thedisk drives 19 ₁-19 ₈ includes a pair of input/output ports A, B. Asnoted above, each one of the FC port by-pass sections 23 ₁-23 ₈ isidentical in construction. An exemplary one thereof, here FC portby-pass section 23 ₁ is shown in FIG. 2 to include: an input/output port30 _(A) coupled to the A port of director 20, and a plurality of, herein this example, eight, output/input ports 32 _(A1)-32 _(A8) seriallyconnected between a first one of the ports, here port A, of theplurality of disk drives 19 ₁-19 ₈ through a plurality of fibre channellinks 29 _(A1)-29 _(A) 8. The fibre channel port by-pass selectorsection 23 ₁ is adapted to couple port A of director 20 ₀ serially to aselected one, or ones, of port A of the plurality of disk drives 19 ₁-19₈ in set 14 ₁ through a first fibre channel comprising one, or more, ofthe plurality of fibre channel links 29 _(A1)-29 _(A8) during a normalmode of operation. The fibre channel port by-pass selector section 23 ₁also has an input/output port 30 _(B) coupled to the A port of director20 ₁ and a plurality of output/ports 32 _(B1)-32 _(B8) seriallyconnected between the B ports of the plurality of disk drives 19 ₁-19 ₈through fibre channel links 29 _(B1)-29 _(B8), as indicated. The fibrechannel port by-pass selector section 23 ₁ is adapted to couple the Aport of director 20 ₁ serially to a selected one, or ones, of the Bports of the plurality of disk drives 19 ₁-19 _(B) in set 14 ₁ through asecond fibre channel comprising one, or more, of the second plurality offibre channel links 29 _(B1)-29 _(B8) in the normal operating mode.

Likewise, fibre channel port by-pass selector section 23 ₂ in FIG. 2 isshown to includes: an input/output port 30 _(A) coupled here, however,coupled to the B port of director 20 ₀ and a plurality of, here in thisexample, eight, output/input ports 32 _(A1)-32 _(A8) serially connectedbetween port A of the plurality of disk drives 19 ₁-19 _(B) in set 14 ₂through a plurality of fibre channel links 29 _(A1)-29 _(A8). The fibrechannel port by-pass selector section 23 ₂ is adapted to couple port Bof director 20 ₀ serially to a selected one, or ones, of port A of theplurality of disk drives 19 ₁-19 ₈ in set 142 through a first fibrechannel comprising one, or more, of the plurality of fibre channel links29 _(A1)-29 _(A8) in section 23 ₂ during a normal node of operation. Thefibre channel port by-pass selector section 23 ₂ also has aninput/output port 30 _(B) coupled to the B port of director 20, and aplurality of output/ports 32 _(B1)-32 _(B8) serially connected betweenthe B ports of the plurality of disk drives 19 ₁-19 ₈ in set 142 throughfibre channel links 29 _(B1)-29 _(B8), as indicated. The fibre channelport by-pass selector section 23 ₂ is adapted to couple the B port ofdirector 20 ₁ serially to a selected one, or ones, of the B ports of theplurality of disk drives 19 ₁-19 ₈ in set 14 ₂ through a second fibrechannel comprising one, or more, of the second plurality of fibrechannel links 29 _(B1)-29 _(B8) in section 23 ₂ in the normal operatingmode.

It is noted that director 20 ₀ is able to access the disk drives 19 ₁-19₈ in set 14 ₂ through its port B in the event of a failure in director20 ₁ and, likewise, director 20 ₁ is able to access disk drives 19 ₁-19₈ in set 14 ₁ through its A port in the event of a failure in director20 ₀.

It is also noted that in the event of a failure of, or removal of, anyone of the port A or port B by-passes 34A, 34B, both sets of disk drives14 ₁ and 14 ₂ are still accessible from one of the directors 20 ₀ and 20₁. For example, if the port A by-pass 34A of fibre channel port by-passsection 23 ₁ fails or is removed, the set 14 ₁ of disk drives isaccessible from director 20 ₁, via the path between port A of director20 ₁, the port B by-pass 34B of fibre channel by-pass section 23 ₁ , andthe port B of the disk drives in set 14 ₁. In like manner, if the port Bby-pass 34B of fibre channel port by-pass section 23 ₁ fails or isremoved, the set 14 ₁ of disk drives is accessible from director 20 ₁,via the path between port A of director 20 ₀, the port A by-pass 34A offibre channel by-pass section 23 ₁, and the port A of the disk drives inset 14 ₁. If the port A by-pass 34A of fibre channel port by-passsection 23 ₂ fails or is removed, the set 14 ₂ of disk drives isaccessible from director 20 ₀, via the path between port B of director20 ₁, the port B by-pass 34B of fibre channel by-pass section 23 ₁, andthe port B of the disk drives in set 14 ₂. In like manner, if the port Bby-pass 34B of fibre channel port by-pass section 23 ₂ fails or isremoved, the set 14 ₂ of disk drives is accessible from director 20 ₀,via the path between port B of director 20 ₀, the port A by-pass 34A offibre channel by-pass section 23 ₂, and the port A of the disk drives inset 14 ₂.

Referring now to FIG. 3, an exemplary one of the FC port by-passsections 23 ₁-23 ₈, here section 23 ₁ is shown in detail connected toset 14 ₁ of disk drives 19 ₁-19 ₈ and to ports A of directors 20 ₀ and20 ₁. As shown also in FIG. 2, the FC port by-pass section 23 ₁ includesa pair of FC port by-passes 34 _(A), 34 _(B). The FC port by-pass 34_(A) is coupled between input/output port 30 _(A) and the A ports of thedisk drives 19 ₁-19 ₈ in set 14 ₁ through fibre channel links 29_(A1)-29 _(A8) and the FC port by-pass 34 _(B) is coupled betweeninput/output port 30 _(B) and the B ports of the disk drives 19 ₁-19 ₈in set 14 ₁ through fibre channel links 29 _(B1)-29 _(B8).

Referring again to FIG. 3, the FC port by-pass 34 _(A) includesselectors 36 _(A1)-36 _(A12) and a control section 40 _(A). (It shouldbe understood that the number of selectors is determined in accordancewith the requisite storage requirements). Each one of the selectors 36_(A1)-36 _(A12) has a pair of input ports (i.e., an A input and a Binput) and an output port, one of the input ports A or B being coupledto the output port selectively in accordance with a control signalC_(A1)-CA₁₂, respectively, fed thereto, as indicated, by the controlsection 40 _(A). It is also noted that input/output port 30 _(A) has aninput port 30 _(A), and an output port 30 _(AO).

It is noted that the selectors 36 _(A1)-36 _(A5); and, 36 _(A8)-36_(A11) are arranged in two selector sections 37 _(A1) and 37 _(A2),Section 37 _(A1) is coupled to disk drives 19 ₁-19 ₄ and section 37_(A2) is coupled to disk drives 19 ₅-19 ₈. Each section 37 _(A1), 37_(A2) is used to control whether one, or more, of the disk drivescoupled thereto should be by-passed. In like manner. the selectors 36_(B1)-36 _(B5); and, 36 _(B8)-36 _(B11), are arranged in two selectorsections 37 _(B1) and 37 _(B2), Section 37 _(B1) is coupled to diskdrives 19 ₁-19 ₄ and section 37 _(B2) is coupled to disk drives 19 ₅-19₈. Each section 37 _(B1), 37 _(B2) is used to control whether one, ormore, of the disk drives 19 ₁-19 ₄, 19 ₅-19 ₈ coupled thereto,respectively, should be by-passed.

Selector 36 _(A1) has its A input connected to input port 30 _(A1) andits B input port connected to output port 30 _(AO). The outputs ofselectors 36 _(A1)-36 _(A11) are connected to the B inputs of selectors36 _(A2)-36 _(A12), respectively. The outputs of selectors 36 _(A1)-36_(A4) and 36 _(A7)-36 _(A10) are also coupled to the A ports of diskdrives 19 ₁-19 ₈, respectively as shown. The output of selector 36_(A12) is connected to the A input of selector 36 _(A6). The output ofselector 36 _(A6) is connected to both the B input of selector 36 _(A1)and the input port 30 _(AI) of director 20 ₀, as indicated. The outputof selector 36 _(A12) is also connected to the A input of selector 36_(A7). The A inputs of selectors 36 _(A2)-36 _(A5) and 36 _(A8)-36_(A11) are fed thereto from the A ports of disk drives 19 ₁-19 ₈,respectively, as indicated. It is noted that the output of selector 36_(A11), in addition to being fed to the B input of selector 36 _(A12) isconnected to an expansion port 30 _(EXAO) and that the A input ofselector 36A₁₂ is connected to an expansion port 30 _(EXAI), for reasonsto be discussed in more detail below in connection with FIGS. 4, 4A and4B.

The FC port by-pass 34 _(B) includes selectors 36 _(B1)-36 _(B12) and acontrol section 40 _(B). Each one of the selectors 36 _(B1)-36 _(B12)has a pair of input ports (i.e., an A input and a B input) and an outputport, one of the input ports A or B being coupled to the output portselectively in accordance with a control signal C_(B1)-CB₁₂,respectively, fed thereto, as indicated, by the control section 40 _(B),It is also noted that input/output port 30 _(B) has an input port 30_(B), and an output port 30 _(BO).

It is noted that the selectors 36 _(B1)-36 _(B5); and, 36 _(B8)-36_(B11) are arranged in two selector sections 37 _(B1) and 37 _(B2).Section 37 _(B1) is coupled to disk drives 19 ₁-19 ₄ and section 37_(B2) is coupled to disk drives 19 ₅-19 ₈. Each section 37 _(B1), 37_(B2) is used to control whether one, or more, of the disk drivescoupled thereto should be by-passed. In like manner. the selectors 36_(A1)-36 _(B5); and, 36 _(A8)-36 _(A11) are arranged in two selectorsections 37 _(A1) and 37 _(A2). Each section 37 _(B1), 37 _(B2) is usedto control whether one, or more, of the disk drives 19 ₁-19 ₄, 19 ₅-19 ₈coupled thereto, respectively, should be by-passed. Selector 36 _(B1)has its A input connected to input port 30 _(B1) and its B input portconnected to output port 30 _(BO). The outputs of selectors 36 _(B1)-36_(B11) are connected to the B inputs of selectors 36 _(B2)-36 _(B12),respectively. The outputs of selectors 36 _(B1)-36 _(B4) and 36 _(B7)-36_(B10) are also coupled to the B ports of disk drives 19 ₁-19 ₈,respectively as shown. The output of selector 36 _(B12) is connected tothe A input of selector 36 _(B6). The output of selector 36 _(B6) isconnected to both the B input of selector 36 _(B1) and the input port 30_(BI) of director 20 ₁, as indicated. The output of selector 36 _(B12)is also connected to the A input of selector 36 _(B7). The A inputs ofselectors 36 _(B2)-36 _(B5) and 36 _(B8)-36 _(B11) are fed thereto fromthe B ports of disk drives 19 ₁-19 ₈, respectively, as indicated. It isnoted that the output of selector 36 _(B11), in addition to being fed tothe B input of selector 36 _(B12) is connected to an expansion port 30_(EXBO) and that the A input of selector 36 _(B12) is connected to anexpansion port 30 _(EXBI), for reasons to be discussed in more detailbelow in connection with FIGS. 4, 4A and 4B.

NORMAL OPERATING MODE

During the normal operating mode, port 30 _(A) of director 20 ₀ iscoupled serially through disk drives 19 ₁-19 ₄ of set 14 ₁ via ports Aof such disk drives 19 ₁-19 ₄ and port 30 _(B) of director 20 ₁ iscoupled serially through disk drives 19 ₅-19 ₈ of set 14 ₁ via ports Bof such disk drives 19 ₅-19 ₈. Such is accomplished by the controlsignals C_(A1)-C_(A12) and C_(B1)-C_(B12) which couple one of the A andB ports of the selectors coupled to the outputs of such selectors in thefollowing TABLE:

TABLE SELECTOR INPUT PORT COUPLED TO SELECTOR OUTPUT 36_(A1) A 36_(A2) A36_(A3) A 36_(A4) A 36_(A5) A 36_(A6) A 36_(A7) B 36_(A8) B 36_(A9) B36_(A10) B 36_(A11) B 36_(A12) B 36_(B1) A 36_(B2) B 36_(B3) B 36_(B4) B36_(B5) B 36_(B6) A 36_(B7) B 36_(B8) A 36_(B9) A 36_(B10) A 36_(B11) A36_(B12) B

In the event of a failure in one of the disk drives 19 ₁-19 ₈, thecontrol sections 40A and 40B are advised of such failure by thedirectors 20 ₀ and 20 ₁ via control lines 45 ₀, 45 ₁, respectively. Forexample, assume there is a failure in disk drive 19 ₃. Once such afailure is detected during the normal operating mode, control section40A changes the logic state on control line C_(A4) to thereby de-coupleinput port A of selector 36 _(A4) from its output and couples input portB of selector 36 _(A4) to its output; thereby by-passing disk drive 19 ₃from the first fibre channel (i.e., the fibre channel through the inputand output ports 30 _(AI) and 30 _(AO) of director 20 ₀). In likemanner, if there is a failure in disk drive 19 ₇, once such a failure isdetected during the normal operating mode, control section 40B changesthe logic state on control line CB_(A10) to thereby de-couple input portA of selector 36 _(B10) from its output and couples input port B ofselector 36 _(B10) to its output; thereby by-passing disk drive 19 ₇from the second fibre channel (i.e., the fibre channel through the inputand output ports 30 _(BI) and 30 _(BO) of director 20 ₁).

FAILURE OF ONE OF THE DIRECTORS 20 ₀ or 20 ₁

As noted above, during normal operation, director 20 ₀ is coupled to theA ports of disk drives 19 ₁-19 ₄ and director 20 ₁ is coupled to the Bports of disk drives 19 ₅-19 ₈. In the event of a failure in director 20₀, director 20 ₀ is de-coupled from disk drives 19 ₁-19 ₄ and director20 ₁ is coupled to the B ports of disk drives 19 ₁-19 ₄ in addition toremaining coupled to the B ports of disk drives 19 ₅-19 ₈. Likewise, inthe event of a failure in director 20 ₁, director 20 ₁ is de-coupledfrom disk drives 19 ₅-19 ₈ and director 20 ₀ is coupled to the A portsof disk drives 19 ₅-19 ₈ in addition to remaining coupled to the A portsof disk drives 19 ₁-19 ₄. Such is accomplished (i.e., removal of faileddirector 20 ₁, for example) by the control signals C_(A1)-C_(A12) andC_(B1)-C_(B12) which couple one of the A and B ports of the selectorscoupled to the outputs of such selectors in the following TABLE:

SELECTOR INPUT PORT COUPLED TO SELECTOR OUTPUT 36_(A1) A 36_(A2) A36_(A3) A 36_(A4) A 36_(A5) A 36_(A6) A 36_(A7) B 36_(A8) A 36_(A9) A36_(A10) A 36_(A11) A 36_(A12) B 36_(B1) B 36_(B2) B 36_(B3) B 36_(B4) B36_(B5) B 36_(B6) A 36_(B7) B 36_(B8) B 36_(B9) B 36_(B10) B 36_(B11) B36_(B12) B

EXPANSION MODE

As described above in connection with FIG. 1, for each redundant FCnetwork 25 ₁-25 ₄ the A port of one of the rear-end directors thereof iscoupled in the normal mode to one disk drive set and the A port of theother one of the rear-end directors thereof is coupled such set of diskdrives. Thus, for example, considering redundant FC network 25 ₁ shownmore clearly in FIG. 2, during the normal operating mode, the A port ofrear-end director 20, and the A port of rear-end director 20 ₁ arecoupled to disk drive set 14 ₁ through port by-passes 34 _(A) and 34_(B), respectively, of port by-pass section 23 ₁. Each one of therear-end directors 20 ₀-20 ₁₅ (FIG. 1) may, however, may be coupled tomore than one disk drive set through the use of additional portby-passes. For example, referring to FIG. 4 and considering port A ofthe rear-end directors 20 ₀ and 20 ₁, an additional disk drive set 14′₁is shown coupled to the A ports of rear-end directors 20 ₀ and 20 ₁through FC port by-passes 34′_(A) and 34′_(B), respectively, as shown.It is first noted that the additional FC port by-passes 34′_(A) and34′_(B) are identical in construction to FC port by-passes 34 _(A) and34 _(B) shown in FIG. 3. Thus, referring also to FIGS. 4 and 4A, thesame numerical designation is used for the elements in FC port by-pass34′_(A) as was used in FC port by-pass 34 _(A) except that the elementsin FC port by-pass 34′_(A) have a prime (′) numerical designation. It isnext noted in FIG. 4, that the A port of director 20 ₀ is connected tothe A ports of the disk drives 19 ₁-19 ₈, 19′₁-19′₈ in both disk drivesets 14 ₁ and 14′₁ through FC port by-passes 34 _(A) and 34′_(A),respectively, and that the A port of director 20 ₁ is connected to the Bports of the disk drives 19 ₁-19 ₈ and 19′₁-19′₈, respectively, in bothdisk drive sets 14 ₁ and 14′₁, respectively, through FC port by-passes34 _(B) and 34′_(B), respectively. More specifically, and referring alsoto FIG. 4A, the output of port A of director 20 ₀ is coupled to port 30_(AI) of FC port by-pass 34 _(A) and the input of port A of director 20₀ is coupled to port 30 _(AO). The output of selector 36 _(A6) iscoupled to the B input of selector 36 _(A1) of port A by-pass 34 _(A),and to port 30 _(A1). Port 30 _(AI) is coupled to the A input ofselector 36 _(A1) of the port A by-pass 34 _(A). The details of the portA by-pass have been described above in connection with FIG. 3. Theoutput of selector 36 _(A11) is connected, through expansion port 30_(EXAO) to A input of selector 36′_(A1) of port A by-pass 34′_(A) andthe output of selector 36′_(A6) of selector 34′_(A) is connected to theB input of selector 36′_(A1) and through port 30′_(AO), to the A inputof selector 36 _(A12) of port A by-pass 34 _(A). Thus, port A by-pass 34_(A) is adapted to service disk drive set 14 and, if expansion isdesired, the additional port A by-pass 34′_(A) is adapted to service theadditional disk drive set 14′₁.

Referring now also to FIG. 4B, the port A by-pass 34 _(A) and theadditional port A by-pass 34′_(A) are shown in more detail. Thus, the FCport by-pass 34 _(A) includes selectors 36 _(A1)-36 _(A12) and a controlsection 40 _(A). Each one of the selectors 36 _(A1)-36 _(A12) has a pairof input ports (i.e., an A input and a B input) and an output port, oneof the input ports A or B being coupled to the output port selectivelyin accordance with a control signal C_(A1)-C_(A12), respectively, fedthereto, as indicated, by the control section 40 _(A). It is also notedthat input port 30 _(AI) is coupled to port A of director 20 ₀ and theoutput of selector 36 _(A6) of by-pass 34 _(A) is coupled to port 30_(AO), as in FIG. 4A.

During the normal mode of operation, port 30 _(A) of director 20 ₀ iscoupled serially through disk drives 19 ₁-19 ₄ of set 14 ₁ via ports Aof such disk drives 19 ₁-19 ₄ and through disk drives 19′₁-19′₄ and thenback to port 30′_(A0). Such is accomplished by the control signalsC_(A1)-C_(A12) and C′_(A1)-C′_(A12) which couple one of the A and Bports of the selectors coupled to the outputs of such selectors in thefollowing TABLE:

TABLE SELECTOR INPUT PORT COUPLED TO SELECTOR OUTPUT 36_(A1) A 36_(A2) A36_(A3) A 36_(A4) A 36_(A5) A 36_(A6) A 36_(A7) B 36_(A8) B 36_(A9) B36_(A10) B 36_(A11) B 36_(A12) A 36′_(A1) A 36′_(A2) A 36′_(A3) A36′_(A4) A 36′_(A5) A 36′_(A6) B 36′_(A7) B 36′_(A8) B 36′_(A9) B36′_(A10) B 36′_(A11) B 36′_(A12) B

In the event of a failure in director 20, director 20 ₀ is coupled tothe A ports of disk drives 19′₁-19′₈ and 19 ₁-19 ₈. Such is accomplishedby the control signals C_(A1)-C_(A12) and C′_(A1)-C′_(A12) which coupleone of the A and B ports of the selectors coupled to the outputs of suchselectors in the following TABLE:

SELECTOR INPUT PORT COUPLED TO SELECTOR OUTPUT 36_(A1) A 36_(A2) A36_(A3) A 36_(A4) A 36_(A5) A 36_(A6) A 36_(A7) B 36_(A8) A 36_(A9) A36_(A10) A 36_(A11) A 36_(A12) A 36′_(A1) A 36′_(A2) A 36′_(A3) A36′_(A4) A 36′_(A5) A 36′_(A6) A 36′_(A7) B 36′_(A8) A 36′_(A9) A36′_(A10) A 36′_(A11) A 36′_(A12) B

It is understood that appropriate control signals are produced by FCport by-passes 34 _(B), 34′_(B) (FIGS. 4, 4A and 4B) to de-couple faileddirector 20 ₁ from the B ports of disk drives 19 ₄-19 ₈ and 19′₄-19′₈.

CONTRACTION MODE

Referring now to FIGS. 5, and 5A, an arrangement is shown where the diskdrive set 14 ₁ in bank 14 (FIG. 1) has 24 disk drives 19″₁-19″₂₄ insteadof the 8 disk drive set 14 ₁-14 ₈ discussed above. Further, a redundantFC network 25″₁ includes, in addition to the rear-end directors 20 ₀ and20 ₁ described above in connection with redundant FC network 25 ₁ (FIG.1), a pair of additional rear-end directors 20″₀ and 20″₁. Director 20″₀is coupled to busses TL and BH (FIG. 1) and director 20″₁ is coupled tobusses TH and BL (FIG. 1). The A port of director 20″₀ is coupled to theA ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₁ throughport A by-pass 34″_(A) of port by-pass section 23″₁ and the B port ofdirector 20″₀ is coupled to the A ports of the disk drives 19″₁-19″₂₄ indisk drive set 14″₂ through port A by-pass 34″_(A) of port by-passsection 23″₂. The A port of director 20″₁ is coupled to the B ports ofthe disk drives 19″₁-19″₂₄ in disk drive set 14″₁₁ through port Bby-pass 34″_(A) of port by-pass section 23″₁ and the B port of director20″₁ is coupled to the B ports of the disk drives 19″₁-19″₂₄ in diskdrive set 14″₂ through port B by-pass 34″_(B) of port by-pass section23″₂. In a manner similar to the redundant FC network 25 ₁ describedabove in connection with FIGS. 1 and 2, the A port of director 20 ₀ iscoupled to the A ports of the disk drives 19″₁-19″₂₄ in disk drive set14″₁ through port A by-pass 34″_(A) of port by-pass section 23″₁ and theB port of director 20 ₀ is coupled to the A ports of the disk drives19″₁-19″₂₄ in disk drive set 14″₂ through port A by-pass 34″_(A) of portby-pass section 23″₂. Likewise, the A port of director 20 ₁ is coupledto the B ports of the disk drives 19″₁-19″₂₄ in disk drive set 14″₁through port A by-pass 34″_(A) of port by-pass section 23″₁ and the Bport of director 20 ₁ is coupled to the B ports of the disk drives19″₁-19″₂₄ in disk drive set 14 ₁t2 through port B by-pass 34″_(B) ofport by-pass section 23″₂.

Thus, here each set of disk drives 14″₁ and 14″₂ may be coupled to fourrear-end directors 20 ₀, 20 ₁, 20″₀, 20″₁. The connections of rear-enddirectors 20 ₀ and 20 ₁ is at the input/output ports 30″_(A), 30″_(B) ofthe port A by-passes 34″_(A), 341″_(B) of port by-pass sections 23″₁ and23″₂, respectively, in a manner similar to that described above inconnection with FIG. 2. The connections of rear-end directors 20″₀ and20″₁ is at the expansion input/output ports 30″_(EXA), 30″_(EXB) of theport A by-passes 34″_(A), 34″_(B) of port by-pass sections 23″₁ and23″₂, respectively, as shown more clearly in FIGS. 5A and 5B.

It is first noted that each of the port A and port B by-passes 34″_(A)and 34″_(B) is identical in construction. An exemplary one thereof, hereport B by-pass 34″_(B) is shown in detail in FIGS. 5B and 5C. Moreparticularly, and referring to FIGS. 5B and 5C, the disk drives19″₁-19″₂₄ are arranged in four sets, each set being coupled to acorresponding one of four selector sections 37″₁-37″₄, as indicated.Thus, disk drives 19″₇-19″₁₂ are coupled to selector section 37″₁, diskdrives 19″₁-19″₁₆ are coupled to selector section 37″₂₁, disk drives19″₁₉-19″₂₄ are coupled to selector section 37″₃, and disk drives19″₁₃-19″₁₈ are coupled to selector section 37″₄, as indicated. Theselectors: 36″_(B2)-36″_(B7); 36″_(B9)-36″_(B14); 36″_(B17)-36″_(B22);and, 36″₂₅-36″_(B30), in the sections 37″₁; 37″₂; 37″₃; and 37″₄,respectively, are controlled by control signals fed to the selectorstherein by control 40″_(B) in a manner similar to that described abovein FIG. 3 in connection with controls 40 _(A) and 40 _(B). Referringalso to FIG. 5C, the port B by-pass 34″ is shown to include, in additionto the selectors in the four selectors sections 37″₁-37″₄, describedabove in connection with FIG. 5B, selectors 36″_(B1), 36″_(B8),36″_(B15), 36″₁₆, 36″₂₃, 36″_(B24), 36″_(B31), and 36″_(B32), arrangedas shown.

Referring again also to FIGS. 5 and 5A, and the exemplary port B by-pass34″_(B), it is noted that port A of rear-end director 20 ₁ is connectedto ports 30 _(BI) and 30″_(BO) of input/output port 30″_(B) and thatport A of rear-end director 20″₁ is connected to ports 30 _(EXI) and30″_(EXO) of expansion port 30″_(EXB). This arrangement is useful whereone has a system with 24 disk dives in each set and then wants to reducethe number of disk drives to either 18, or 12, or 6 disk drives.

More particularly, and referring also to FIG. SD, rear-end director 20 ₁a configurations is shown where director 20 ₁ is coupled to the B portsof all 24 disk drives 19″₁-19″₂₄ in set 14″₁ and director 20″₁ is notcoupled to any of the 24 disk drives 19″₁-19″₂₄ in set 14′₁. Thus, theoutput of selector 36″_(B1) is coupled to its input port A (as indicatedby the arrows 50), the output of selector 36″_(B8) is coupled to its Ainput port, the output of selector 36″_(B15) is coupled to its A port,the output of selector 36″₁₆ is coupled to its B port, the output ofselector 36″₂₃ is coupled to its A port, the output of selector36″_(B24) is coupled to its B port, the output of selector 36″_(B31) iscoupled to its B port, and the output of selector 36″_(B32) is coupledto its A port.

Thus, the A port of director 20 ₁ connected to the port 30″_(BI) passesthrough selector 36″_(B1) to the input of selector section 37″₁. Theoutput of selector section 37″₁ then passes successively through: theselector 36″_(B8); selector section 37″₂; selector 36″_(B16); selectorsection 37″₃; selector 36″_(B24); selector section 37″₄; selector36″_(B31); selector 36″_(B23); selector 36″_(B15); selector 36″_(B32),then to port 30″_(BO) and back to the A port of director 20 ₁. It isnoted that director 20″₁ is by-passed and not connected to the selectorsections 37″₁-37″₂ and hence not connectable to the disk drivesconnected to such selector sections 37″₁-37″₂.

If the user wishes to reduce the number of disk drives coupled todirector 20 ₁ from 24 to 18 with director 20″₁ coupled to the other 6disk drives, such a configuration is shown in FIG. 5E. Thus, the outputof selector 36″_(B1) remains coupled to its input port A (as indicatedby the arrows 50), the output of selector 36″_(B8) remains coupled toits A input port, the output of selector 36″_(B15) remains coupled toits A port, the output of selector 36″₁₆ remains coupled to its B port,the output of selector 36″₂₃ switches to its B port, the output ofselector 36″_(B24) switches to its A port, the output of selector36″_(B31) switches to its A port, and the output of selector 36″_(B32)remains coupled to its A port.

Thus, the A port of director 20 ₁ coupled to port 30″_(BI) is thencoupled through selector 36″_(B1) to the input of selector section 37″₁.The output of selector section 37″₁ then passes successively through:the selector 36″_(B8); selector section 37″₂; selector 36″_(B16);selector section 37″₃; selector 36″_(B23); selector 36″_(B15); selector36″_(B32) and then to port 30″_(BO) and back to the A port of director20 ₁. The A port of director 20″₁ is connected through selector36″_(B31) and through selector 36″_(B24) to selector section 37″₄ andthe back to the A port of selector 20″₁.

If the user wishes to reduce the number of disk drives coupled todirector 20″₁ from 18 to 12 with the director 20″₁ being coupled to theother 12 disk drives, such a configuration is shown in FIG. 5F. Thus,the output of selector 36″_(B1) remains coupled to its input port A (asindicated by the arrows 50), the output of selector 36″_(B8) remainscoupled to its A port, the output of selector 36″_(B15) switches to itsB port, the output of selector 36″₁₆ switches to its A port, the outputof selector 36″₂₃ switches to its A port, the output of selector36″_(B24) switches to its B port, the output of selector 36″_(B31)remains at its A port, and the output of selector 36″_(B32) remains atits B port.

Thus, the A port of director 20 ₁ coupled to port 30″_(BI) is coupledthrough selector 36″_(B1) to the input of selector section 37″₁. Theoutput of selector section 37″₁ then passes successively through: theselector 36″_(B8); selector section 37″₂; selector 36″_(B15); selector36″_(B32) and then to port 30″_(BO) and back to the A port of director20 ₁. The A port of director 20″₁, connected through selector 36″_(B31)is coupled through selector 36″_(B31) then through selector 36″_(B23);selector 36 _(B16); selector section 37″₃, then through selector36″_(B24), selector section 37″₄ and the back to the A port of selector20″₁.

If the user wishes to reduce the number of disk drives coupled todirector 20 ₁ from 12 to 6 with the director 20″₁ being coupled to theother 18 disk drives, such a configuration is shown in FIG. 5G. Thus,the output of selector 36″_(B1) remains coupled to its input port A (asindicated by the arrows 50), the output of selector 36″_(B8) is switchedto its B port, the output of selector 36″_(B15) is switched to its Bport, the output of selector 36″₁₆ is switched to its B port, the outputof selector 36″₂₃ remains at its A port, the output of selector36″_(B24) remains at its B port, the output of selector 36″_(B31)remains at its A port, and the output of selector 36″_(B32) is switchedto its A port.

Thus, the A port of director 20 ₁ coupled to port 30″_(BI) is coupledthrough selector 36″_(B1) to the input of selector section 37″₁. Theoutput of selector section 37″₁ then passes through selector 36″_(B32)and then to port 30″_(BO) and back to the A port of director 20 ₁. The Aport of director 20″₁ connected through selector 36″_(B31) is coupledthrough selector 36″_(B31) then through successively through selector36″_(B23); selector 36 _(B15), selector section 37 ₂, selector 36_(B16), selector section 37″₃, selector 36 _(B24), to selector section37″₃, then through selector 36″_(B24) to selector section 37″₄ and theback to the A port of selector 20″₁.

Other embodiments are within the spirit and scope of the appendedclaims.

What is claimed is:
 1. A fibre channel port by-pass selector section,comprising: a pair of port by-passes, each one of such by-passes,comprising: (a) a bi-directional input/output port; and (b) a pluralityof bidirectional output/input ports, wherein: the bidirectionaloutput/input ports of a first one of the pair of port by-passes areserially connected between a first one of a pair of bi-directional portsof a plurality of disk drives through a first plurality of fibre channellinks, and the bi-directional output/input ports of a second one of thepair of port by-passes are serially connected between a second one ofthe pair of bidirectional ports of the plurality of disk drives througha plurality of second fibre channel links; wherein the fibre channelport by-pass selector section is adapted to couple the input/output portof the first one of the pair of port by-passes serially to a selectedone, or ones, of the plurality of disk drives through a first fibrechannel via the first one of the pair of bidirectional ports of theplurality of disk drives, such first fibre channel comprising one, ormore, of a first set of the plurality of fibre channel links; whereinthe fibre channel port by-pass selector is adapted to couple theinput/output port of the first one of the pair of port by-passesserially to a selected one, or ones, of the plurality of disk drivesthrough a second fibre channel via the second one of the pair ofbi-directional ports of the plurality of disk drives, such second fibrechannel comprising one, or more, of a second set of the plurality offibre channel links; and wherein the first fibre channel and the secondfibre channel provide separate fibre channels to and from the pluralityof disk drives and wherein the first and second fibre channels includesthe same disk drives in the plurality of disk drives.
 2. A system,comprising: a pair of directors, each one having a pair ofbi-directional ports; a pair of fibre channel port by-pass sections,each one thereof having a pair of port by-passes; and a pair of sets ofdisk drives, each one of the disks in the pair of sets having a pair ofbidirectional ports; wherein: a first one of the port by-passes in afirst one of the port by-pass sections comprises: (a) a plurality offirst ports, each one being coupled to a first one of the pair ofbi-directional ports of a corresponding one of the disk drives in afirst one of the pair of sets of disk drives through a first fibrechannel; and (b) a second port coupled to a first one of the pair ofbi-directional ports of a first one of the directors; a second one ofthe port by-passes in the first one of the port by-pass sectionscomprises: (a) a plurality of first ports, each one being coupled to asecond one of the pair of bi-directional ports of a corresponding one ofthe first one of the pair of sets of the disk drives through a secondfibre channel; and (b) a second port coupled to a first one of thebidirectional ports of a second one of the directors; a first one of theport by-passes in a second one of the port by-pass sections comprises:(a) a plurality of first ports, each one being coupled to a first one ofthe pair of bi-directional ports of a corresponding one of a second oneof the pair of sets of the disk drives through a third fibre channel;and (b) a second port coupled to a second one of the pair of ports ofthe first one of the directors; and a second one of the port by-passesin the second one of the port by-pass sections comprises: (a) aplurality of first ports, each one being coupled to a second one of thepair of bi-directional ports of the a corresponding one of the secondone of the pair of sets of the disk drives through a fourth fibrechannel; and (b) a second port coupled to a second one of the pair ofbi-directional ports of the second one of the directors; and wherein thefirst, second, third and fourth fibre channels provide separate fibrechannels to and from the pairs of sets of disk drives and wherein thefirst and second fibre channels include the same disk drives the firstone of the pair of sets of disk drives and wherein the third and fourthfibre channels includes the same disk drives in the second one of thepair of disk drives.
 3. A system, comprising: a pair of directors; apair of port by-passes; and a set of disk drives, each one of aplurality of disk drives in the set having a pair of bi-directionalports; wherein: a first one of the pair of port by-passes has aplurality of first ports, each one being coupled to a first one of thepair of bi-directional ports of a corresponding one of the disk drivesand a second port coupled to a first one of the directors through afirst fibre channel; a second one of the pair of port by-passes having aplurality of first ports, each one being coupled to a second one of thepair of bi-directional ports of a corresponding one of the disk drivesand a second port coupled to a second one of the directors though asecond fibre channel; and the first and second fibre channel provideseparate channels to and from a corresponding one of the bi-directionalports of the disk drives and wherein the first and second fibre channelsincludes the same disk drives in the plurality of disk drives.